keystone keeps a lot of CPU during nova rally scenario

[Leontii Istomin]

We have found that keystone keeps up to 900% CPU during boot_and_list_server_batch_x10 rally scenario.
atop from node-199: http://paste.openstack.org/show/325031/
atop from node-206 http://paste.openstack.org/show/325032/
atop from node-225 http://paste.openstack.org/show/325034/
We seen CPU load during ~3 minutes. At the time nova couldn't answer requests (500 HTTP)
http://paste.openstack.org/show/324755/
We can't reproduce the issue anymore.
Diagnostic Snapshot (needed logs have been deleted by logrotate, but atop binarys are there): http://mos-scale-share.mirantis.com/fuel-snapshot-2015-06-29_11-25-54.tar.xz

[Dina Belova (dbelova)]

One more similar issue happened before - https://bugs.launchpad.net/mos/+bug/1467594 - I marked the old one as a duplicate for this one, probably more details can be found in https://bugs.launchpad.net/mos/+bug/1467594